Core-Based Trees

Core-Based Trees
When we discussed shared trees, you learned that there were two types: unidirectional and bidirectional.
CBT utilizes the bidirectional method for its multicast data distribution. Because CBT
uses a shared tree system, it designates a core router that is used as the root of the tree, enabling
data to flow up or down the tree.
Data forwarding in a CBT multicast system is similar to the shared tree distribution we described
earlier. If a source to a multicast group sends multicast data to the CBT-enabled router, the router
then forwards the data out all interfaces that are included in the tree, not just the interface that leads
to the core router. In this manner, data flows up and down the tree. After the data gets to the core
router, the core router then forwards the information to the other routers that are in the tree.
Figure 19.20 depicts this process.